Organic fluorescent compounds, also referred to as dyes, are used as sensitive detection reagents in biological assays. Xanthene-type dyes are commercially available as research reagents from a number of manufacturers.
Fluorescein derivatives of these compounds are based on the 3H-xanthene-6-ol-3-one core structure, with a 2-carboxyphenyl group at C9 of the central ring. Rhodamine dyes typically have a 6-amino-3H-xanthene-3-imine core structure with the same 2-carboxyphenyl group at C9. Rhodol based dyes have a central 6-amino-3H-xanthene-3-one structure with the same 2-carboxyphenyl group at C9.
Adding negatively charged sulfonate groups to fluorescent dyes increases their water solubility, facilitating use in biological applications and reducing dye-dye interactions due to like charge repulsion. Sulfonation has been used to modify cyanine dyes (U.S. Pat. Nos. 5,268,486; 5,486,616; 5,569,587; and 5,569,766) and xanthene-type dyes (U.S. Pat. No. 6,130,101).
Additional compounds, compositions, and methods are desirable.